1. Field of the Invention
The present invention relates to a recording technology employing an ink-jet recording method as a means for obtaining pictures, color graphics, or color hard-copies produced from computer graphics, color CRT displays, or the like and; more specifically, to an ink-jet recording technology which can reproduce color images that are faithful to the original, while maintaining clearness and high density.
2. Description of the Related Art
An ink-jet recording method has been used for terminal printers of word-processing machines and computers, copying machines, facsimile machines, or the like, due to its low noise, low operational cost, feasibility of downsizing, ease of color recording, and the like.
Generally, a color ink-jet recording method employs three primary colors, i.e., cyan, magenta, and yellow, and may further add black as a fourth color.
In the conventional ink-jet recording method, it was necessary to use a specific type of paper having an ink absorption layer to obtain a highly developed color-image with no blurring of ink. However, due to the recent improvement of ink, plain paper being suitable for ink-jet printing, which is used for printers and copying machines in large quantity, has been put into practical use. However, it is widely recognized that the printing quality of plain paper is still inadequate. The biggest reason for this deficiency is an incompatibility between the incidence of blurring and recording quality of a black image (particularly, recording quality of black letters), in which the blurring occurs between different color inks, which is referred to as bleeding.
As disclosed in Japanese Laid-Open Publication No. #55-29546, quick-drying ink having a high penetration rate on plain paper is generally used to produce a color image on plain paper by means of the ink-jet recording method. A high-quality image without bleeding incidence can be obtained by using the above-mentioned ink. However, such ink has a low image-density and further tends to allow so-called feathering in which the ink blurs slightly along fibers in paper in the periphery of each color image. Even though such feathering may be barely noticeable in a color image area, it is conspicuous in a black image area thereby causing deterioration in printing quality. The printing quality becomes poor especially when the black image is formed by black letters which become illegible due in part to a lack of sharpness.
To overcome the above-described ink inferiority, and to obtain an image having decreased feathering and also having much higher density and high quality, it is necessary to use black ink having a relatively slow penetration rate on plain paper. In this case, however, each ink may blur at the adjacent boundary portion of the recording image areas where black and color inks meet.
There is a "trade off" relationship between the prevention of blurring between black ink and color inks and the improvement of quality of the color image obtained by the reduced incidence of feathering in the black image.
According to Japanese Laid-Open Publication No. #4-158049, a combined use of print heads of a plurality of colors for color recording and a print head for letter recording has been proposed, in which the use of these two different heads are switched according to the recording image. However, disadvantages such as high cost and the inevitability of large-sized apparatus are unavoidable in this method because the head for letter recording is used in combination with the conventional heads of a plurality of colors for color recording.